


Nesting on the Edge of Sanity

by NihilismPastry



Series: Commissions [7]
Category: Undertale (Video Game)
Genre: Alternate Universe - Horrortale, Biting, Bondage, Female genitalia, Knotting, Marking, Monster Heat, Nesting, Other, gender neutral reader
Language: English
Status: Completed
Published: 2017-08-30
Updated: 2017-08-30
Packaged: 2018-12-21 19:12:01
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,510
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11950806
Author URL: https://archiveofourown.org/users/NihilismPastry/pseuds/NihilismPastry
Summary: Sans goes through his yearly heat, and you're stolen along for the ride...Kinda.





	Nesting on the Edge of Sanity

**Author's Note:**

> Gore Level: Very Low

Sans could feel it deep in his bones, pulsing and swirling in a frenzy that threatened to throw him into the abyss of madness itself. It had started with small things, pressing his distal phalanges into the soft flesh of their skin, smelling their hair when they would hug him, insisting they sit on his lap when they watched the sun rise every morning. They took it as small, romantic gestures spawned from living on the surface over the past five years, and acclimating to the ways humans did things in their romantic relationships.

Did he fucking wish that was the case.

The next few days it got worse. He would demand they took a shower the minute they came home, and would scrub them down himself, and would insist they wear his clothes until bed. He would then insist they took off his clothes, and go to his room instead of their own. Cooking became part of his daily routine, and he always ensured they ate every crumb, before allowing them to leave anywhere. Petting, kissing, and biting them was becoming more frequent, and he couldn’t help but bend them over the table, and fucking their brains out before they left for work each morning, cum stuffed in their pussy throughout the day.

When it got to the point he was cleaning the house, his brother left to go stay with a few friends, giving Sans a little more peace of mind. All of the clothes and sheets were washed, and he even scrubbed at the couch and carpet. He found that he liked the way the basement smelled, less like anyone else and mostly him, so he took the laundered blankets and sheets down there, creating a small lump in the middle of the room. It needed food too, and some other things that would make his mate happy. Yes, that’s all he needed right now, his mate comfortable, in his nest, and happy.

But then things went from weird, to batshit crazy.

* * *

You woke up to feeling something cold and heavy around your wrists. They felt suspiciously like handcuffs, and your tired mind was already slurring together curses at the thought. You knew Sans had some weird as fuck kinks, but you were still sore from yesterday, somnophilia was too much for you right now. “Sans, stop…”

You felt cold bones pet your stomach, and heard a hiss that reminded you of a pissed off cat. You cracked open an eye, just to see your boyfriend peering over you, his red pupil blown wide open. He pressed at you stomach again, successfully flipping you over and onto your back, your legs splayed. You blinked a little more, and wriggled, your eyebrows furrowing as you realized you weren’t on the bed. In fact, upon looking around, you realized that you weren’t even in your room. You tilted your head back, and your eyes widened when you saw the hot water heater behind you. “Why’re we in the basement?”

He doesn’t answer you, well not with words, instead his ribs rattled and he makes a low grunt, before sitting himself between your legs. His dick was there, and the dark blue magic pulsed and writhed, looking a little more alive than you were comfortable with. He rakes his fingers along your stomach again, a low purr coming deep from his throat, before he juts his hips forward. His tip slides easily between your folds, and you hiss, he’d somehow grown in the middle of the night. He continued pushing into you, his throaty moans and the scraping against your hips as he fought to push himself inside you felt divine. Your toes curled when he finally managed to hilt all the way inside you, and began a rough pace. You tried to grab him, maybe get some form of affection, but your arms jerked and you couldn’t move them much further. It was a rough and sloppy coupling, at some point he had bent down and began licking at his mark on your shoulder, that purring coming back with a vengeance. Your toes curled and your back arched as he dragged you closer and closer to that orgasm. Finally you felt him spurt deep inside you, the intense heat of his cum, and the bite on your shoulder finally allowing you to have your own orgasm.

You stared up at the skeleton, who was now knotted inside of you. “So are you just…” You didn’t even know what to say, honestly. “Have you at least called my boss to let her know I can’t make it?”

You only got a purr in reply.

* * *

Over the next few days a pattern began. You’d wake up to getting fucked, then have his knot tied to you for an hour. Afterwards he’d dig some food out from the many blankets and pillows taking up the floorspace of the basement, and fed you enough to make your stomach cramp. Anytime you had to use the toilet, he’d follow you around, even sitting in front of you the entire time. He wouldn’t allow you to shower, much to your chagrin, and would fuck you between sleeping on your stomach, and eating some food himself. Most of his speech was gone, he’d attempt to talk to you in a series of grunts, purrs, and bone rattling that you still couldn’t understand. Sometimes he’d bite you for no particular reason, other times he’d insist on licking your body, or just cumming all over you.

Despite all this he was oddly attentive. You were very used to an aloof Sans, one that often had his skull in the clouds, and the only thing that could drag him back down was food and his brother. You weren’t used to this Sans, who took care of your every need, and insisted on touching you in some form or fashion throughout the day. Not that you were complaining, you weren’t going to say know to some time off of work, but his sudden shift in behavior just felt so wrong. You hummed as he began eating you out for the third time today, his fingers clawing at your thighs, and his ribs clacking together. It didn’t take you long to cum, your body was over stimulated, and the way his tongue curled around your clit was downright sinful. You came with a shuddering cry, the pulsing warmth of the orgasm rolled through your body, and left you a panting mess as the Monster above you settled himself onto your chest. You pet his skull gingerly, being mindful of the gaping hole, and he let out a soft trill at your affection.

“You know I love you, right?” You said quietly. “I dunno if you even understand me anymore. What you did was pretty scary, at first. I honestly thought you were gonna eat me or something.” His red pupil stared at you, focused entirely on your lips. If you didn’t know any better, you’d think he was actually paying attention to what you were saying. “But i’ve never been cared for so well in my life, I mean despite the obvious, you’re kinda coddling me. I didn’t expect something like that out of you.”

A long royal blue tongue slipped out of his mouth, and began laving at your neck, his hands trailing down your sides until they curved and cupped your ass. You knew exactly where this was going, where anything went with Sans lately, and spread your legs wide for him. You could feel the warmth of his magic against your thigh, and hissed as he hilted himself into your tight cunt in one go. You whined at the rough treatment, but he ignored it, setting up a fast pace that had your body rocking into the warm blankets, and your hands clawing at his shoulders. He growled, and hissed, the pattern once again reminding you of words. Your legs slipped up, and around his hips, pulling him deeper into your needy pussy.

You chanted his name like a mantra as he fucked you raw. His fingers left bruises and cuts on your chest, and you felt that cold tongue of his lick up any of the blood that welled up to the surface. You wriggled underneath him, trying to finally get him to cum, give him some form of relief so he would leave you alone for just a little bit longer while he was tied to you. His spine curled and his shoulders hunched as he picked up his pace, his jaws snapping open wider, and drool splattering onto your abused chest. You leaned up and pressed your mouth to his, effectively swallowing his tongue, and that got him to stop completely. Sans had never been one for straight on kissing, not minding a peck to his teeth, but always finding it uncomfortable to kiss you with tongue. It seemed, even in this horny mindset, that aspect was certainly still there as he pulled back away from you with a growl.

You hissed as he pulled out of you, and pushed your body away from his. You scrambled to sit up, but his cold hands grabbed at your hips, and turned you over completely. A hand pinned you to the floor by the next, and the other dragged your ass into the air. You heard his ribs rattle, before his dick was plunged into your body once again. In this position he could dive deeper into you, and it helped that he insisted on dragging your hips to meet him for every thrust. Your fingers curled into a ball, and you allowed him to ride you, just enjoy the pleasure that was beginning to curl and twist inside your abdomen. Your eye fluttered shut, and your toes curled, a hiss making its way through your throat as your walls clamped down on him. The skeleton purred above you, and removed the hand from your neck, letting you lay like a used up doll while he used his other hand to grip your hips properly. You could feel his dick getting unnaturally warm, before you felt him ramming into you, forcing that knot into your abused pussy.

Your back arched again as another, albeit smaller, orgasm rocked your body. This seemed to help trigger Sans’ own orgasm, as ropes of warm cum spurt inside your body. You whined as he leaned his weight into you, his ribs digging into your skin, likely leaving even more bruises and cuts, but he didn’t seem to care as he nuzzled his nasal ridge into your neck, a soft purring coming from deep inside his ribs. You could even feel them shift and vibrate, which would have been nice if they weren’t scratched and scarred. “You’re a mess, ya know that?”

He only trilled back to you, his tongue licking at some blood that was leaking down your black. The position you held was uncomfortable, but you were just grateful when that knot finally deflated, and he slipped himself out of you. Cum gushed between your legs, and stained the thick blanket, soaking it further with the pungent magic. You flipped onto your back, and shut your eyes, ready to fall back to sleep, and take a short break. You limbs were sore, and so was your pussy. You were also pretty sure that Sans had eaten part of your shoulder, it was burning too much for there just to be a bite mark.

You grunted when you felt a heavy and cold body drop on top of yours. You cracked open an eye, just to see Sans nuzzling into your chest, his sockets shut. It only took a few moments for him to fall asleep, his body completely going still, looking far too close to a corpse for comfort. You didn’t get long to dwell on it though, your eyes shutting as your arms looped around his pelvis, holding him close.

* * *

You whined as the dick prodded at your abused pussy, fingers were curled around your wrists, pinning you in place. Sans was less likely to follow you to the bathroom, or insist on feeding you now, and had even started talking again, but he still fucked you constantly. In fact, it felt like it was more frequent over the course of the last three days. “look at this pussy, all stretched and gushin’ with my cum.” You writhed beneath him when he finally bottomed out inside you. “bet you were dreamin’ ‘bout it last nigh, hm?”

No, you were dreaming about pizza, but you didn’t want to completely ruin the mood. Two weeks in what Sans had fondly called his ‘nest’, was starting to wear you down. While Sans did take good care of you, the outside world was calling your name. Work needed to be done, the sky stared at, and maybe a quick romp in the snow to ice down you abused muscles. You didn’t even mourn the fact you didn’t cum when the skeleton rammed his knot inside you, tying you both together for the next thirty-three minutes. Yes, you’ve done this so many times you had the time down to a fucking science. While your lover filled you with more of his cum, his hand idly drumming on your stomach, the other kept himself propped up. You were pretty thankful for that one, you honestly could live the rest of your life without the skeleton’s ribs digging into your skin. “So this is almost over, huh?”

“for the most part, yeah.” He shut his sockets. “it uh, the heat lasts two weeks.i lose my mind, then get it back towards the end. don’t remember jack shit between point a and b.” He cracked open his good socket, the moderate sized pupil looking you over. “got all your parts, so couldn’t been that bad.”

“I’ve had nonstop sex, you were kinda crazy, and I haven’t had a shower in forever.” You shuddered, the stickiness of cum and sweat clinging to you like a second skin at this point. “I’d been fine if you let me take a bath at least. But no, sex was more important.”

He chuckled, the deep sound making you rub your thighs together. Maybe you actually wanted that orgasm after all…”sounds like ya had a good time then.” He nuzzled his nasal cavity into that familiar spot on your neck. maybe i’ll snag ya for my summer cycle.”

“God please no.”

“fuck that sweet ass of yours in a new nest.” You heard him purr. “gettin’ horny just thinkin’ ‘bout it.”

“Or, ya know, you could clean this one up while I’m in the shower." You said. "It’ll be good as new.”

“i’ll think about it.”

You shuddered as he pulled his dick out of you, and carefully deposited your body on top of his, cold fingers moving down and grabbing your ass, and kneading the soft flesh. “Hey, Sans?”

“hm?”

“Love you.”

His teeth pressed to your forehead, a faint tingle of magic warming the spot. “love ya too.”

**Author's Note:**

> And that's it for this commission! I love writing a nesting Axe, it's just so cute, and I can imagine him doing this sort of thing for his mate. Maybe uh, a little more...weird in the Underground, but thank God for the surface and therapy, right? Anyway, like I said, I love writing Axe, so this was a fun job. 
> 
> Know what isn't fun? My tumblr! nihilismpastry.tumblr.com


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